//code to check if a value exists in an array using javascript indexOf var fruits_arr = ['Apple', 'Mango', 'Grapes', 'Orange', 'Fig', 'Cherry']; var string = "Orange"; // Find in Array fruits_arr.indexOf('Tomato'); fruits_arr.indexOf('Grapes'); // Find in String string...
Output: Add value if not exists Loop through the array to check whether a particular username value already exists and if it does do nothing, but if it doesn’t add a new object to the array. const arr = [{ id: 1, username: 'fred' }, { id: 2, username: 'bill' }, { ...
You can use the indexOf() method to check whether a given value or element exists in an array or not. The indexOf() method returns the index of the element inside the array if it is found, and returns -1 if it not found. Let's take a look at the following example:...
constobj={name:'Alice',age:30,city:'New York'};// 使用 for...in 循环遍历for(letkeyinobj){if(obj.hasOwnProperty(key)){console.log(`Key:${key}, Value:${obj[key]}`);}}// 使用 Object.keys() 遍历Object.keys(obj).forEach(key=>{console.log(`Key:${key}, Value:${obj[key]}`...
constexists=x=>x!=null;constifExists=value=>exists(value)?Promise.resolve(value):Promise.reject(`Invalid value:${value}`);ifExists(null).then(log).catch(log);// Invalid value: nullifExists('hello').then(log).catch(log);// hello ...
functionexists(value){returnx!=null?Promise.resolve(value):Promise.reject(`Invalid value:${value}`)}asyncfunctionfoo(num){returnexists(num).then(v=>23*v)} 通过这种方式就可以把来自exists中的catch方法委派到调用foo的函数中: 代码语言:javascript ...
Thehas()method returnstrueif a specified value exists in a set. Example // Create a Set constletters =newSet(["a","b","c"]); // Does the Set contain "d"? answer = letters.has("d"); Try it Yourself » The forEach() Method ...
In addition, empty JavaScript objects can have the valuenull. This can make it a little bit difficult to test if an object is empty. You can test if an object exists by testing if the type isundefined: Example: if(typeofmyObj ==="undefined") ...
. The first function will return1or0if a value that is passed exists in an array of simple values. If the value exists, the function will return1, and if the value does nto exist in the array, it will return0. Let’s look at the code to create a function namedarrayContainsValue....
let apiResponse = fetch("https://fjolt.com/api").then(res => res.json()).then((data) => { return data;});// Now contains a JSON object - assuming one exists1.2.3.4.JavaScript Fetch 的选项 由于Fetch 可以发送和接收 HTTP 请求,当我们想要使用它获取 URL数据的时候,还可以带一些选项,即...